1. Field of the Invention
The present invention relates to a method and apparatus for manufacturing drum and flexible belt charge receptors for photocopiers. More particularly, the invention relates to an efficient method and a modular thermal circumference dryer for processing cylindrical or belt-like substrates to apply a coating material to the substrate.
2. Description of Related Art
A photoreceptor is a cylindrical or belt-like substrate used in a xerographic apparatus. The photoreceptor substrate is coated with one or more layers of a photoconductive material, i.e., a material whose electrical conductivity changes upon illumination. In xerographic use, an electrical potential is applied across the photoconductive layer and then exposed to light from an image. The electrical potential of the photoconductive layer decays at the portions irradiated by the light from the image, leaving a distribution of electrostatic charge corresponding to the dark areas of the projected image. The electrostatic latent image is made visible by development with a suitable powder. Better control of the coating quality yields better imaging performance.
One method of coating substrates is to dip the substrate in a bath of the coating material. This method is disadvantageous because it usually results in a non- uniform coating. In particular, when the substrate is oriented vertically and dipped into a bath, the coating thickness tends to "thin" or decrease at the top of the substrate and "slump" or increase at the base of the substrate due to gravity induced flow of the coating material as the substrate is lifted from the bath. Thickness variations also occur even when the photoreceptor is oriented horizontally and dipped into the bath due to the formation of a meniscus as the substrate is removed from the bath. This variation in coating thickness causes variations in the performance of the photoreceptor.
In another method, an air assisted automatic spray gun uses high velocity air to atomize the coating formulation which is sprayed onto a substrate. Due to high mass transfer rates intrinsic to the use of atomizing air, this method entails considerable evaporative loss of solvent from the spray droplets and requires the use of slow evaporating solvents to prevent excessive solvent loss before the droplets arrive at the substrate. It is difficult to use this method in a sealed environment, and thus difficult to control the solvent humidity surrounding the substrates prior to, during, or after the coating process. In addition, the air atomized spray method creates a considerable amount of overspray which results in higher material usage.
U.S. Pat. No. 4,456,632 to Amberkar discloses a method and apparatus for fabricating electrosensitive paper with a white finish comprising a base layer of paper, a solvent-based resin coating, and a thin layer of aluminum, optionally including a white overcoat. The patent states that a mixture of solvents, having different evaporation rates, are employed to provide a white appearance and that the mixture may include a volatile true solvent as well as a less volatile diluent. The patent discloses that after the application of the resin coating to the paper base, the solvents are evaporated by a three- stage drying process where the first stage involves an elevated temperature with turbulent air flow.
U.S. Pat. No. 4,975,352 to Anayama et al discloses an electrophotographic photosensitive member comprising a conductive support, and having thereon a charge generation layer formed by coating, and then followed by drying, and further comprising a charge transport layer formed by coating, and then followed by drying. The patent states that the drying process is carried out by heating a freshly dipped cylinder at 80.degree. C. for 10 minutes.
U.S. Pat. No. 4,543,314 to Maxwell discloses a process for preparation of an electrostatographic photosensitive device comprising: (1) combining a sodium additive with trigonal selenium particles, an organic resin binder and a solvent for the binder to form a milling mixture, (2) milling the mixture to form a uniform dispersion, (3) applying the dispersion to a substrate, and (4) drying the layer. The patent states that in the prior art the trigonal selenium layer can be dried at 60.degree. C. in a forced air oven for 18 hours, and discloses that conventional drying methods can be employed such as oven drying, radiant heat drying, forced air drying and the like.
U.S. Pat. No. 4,069,356 to Fischer discloses a method for rapidly forming photoconductive layers for integrated circuits wherein powders of component materials are mixed with a copper halide powder and formed into pellets. The pellets are used as an evaporant source for vacuum deposition of a photoconductive layer onto a prepared substrate. The patent states that the photoconductive layer and substrate are then baked in an oxygen- rich atmosphere at a temperature between 300.degree. and 550.degree. C.
U.S. Pat. No. 4,855,203 to Badesha et al discloses a layered photo responsive imaging member comprised of: (1) a supporting substrate, (2) an amorphous photoconductive layer, and (3) a hole transporting layer dispersed in a resinous binder. The patent states that a solution is deposited on the supporting substrate and subsequently heated to dry the layer to the member.
U.S. Pat. No. 4,943,447 to Nelson et al discloses a process for heat treating a coating applied to an automobile body which is carried out with an apparatus comprising radiant heating elements for generating radiant heat in a predetermined path and convection heating elements for generating a flow of heated air.
The related art described above does not disclose a manufacturing process or apparatus for practicing the manufacturing process with low cost high quality efficient drying of dipped photoreceptors.